My MCU (2015 S85 D) was replaced under warranty (extended) yesterday after episodes of losing the NAV screen, then the screen behind the wheel, then difficulties in waking up the vehicle. The Tesla Service center at Scottsdale was very professional and thorough,. I am totally pleased with the result.
I am assuming that the replacement was a reconditioned unit. It was described on the invoice as:
MCU, MDLX,NA, PREMIUM,REMAN (1098010-00-F).
Note:such a change causes the vehicle to lose its data cache, so all settings are lost, as is memory for previous earnings.